Many techniques have been developed to non-invasively image or "see" the internal structures of human and animal bodies. Such techniques have in the past included radiography, fluoroscopy, and, more recently, ultrasonography, computed tomography, and magnetic resonance imaging. Prior to the development of these imaging techniques, exploratory surgery had to be performed in order to see the internal structures of human and animal bodies. However, fatal complications were sometimes encountered with exploratory surgery.
Despite the advances that have been made in the above imaging techniques, many entities are difficult to differentiate using only imaging techniques. Accordingly, it is often very difficult to conclusively diagnose certain conditions based solely on their image. Only by obtaining a sample of the involved tissue or fluid can the condition or entity be conclusively identified, and the correct diagnosis made.
In attempt to avoid the dangers associated with surgery, a number of minimally invasive techniques for obtaining tissue or fluid samples from the body have been developed in recent years. These techniques involve the use of imaging techniques, such as ultrasound, to guide specially designed needles through the inside of the body to the target tissue or fluid. Once guided to the target, the specially designed needle is used to obtain samples of the target tissue or fluid for analysis outside of the body. Moreover, in certain circumstances, a tube or catheter may be installed at the target for longer term fluid drainage or for administering therapeutic agents. Many lives have been saved and surgical complications avoided by the use of such imaging guidance techniques for obtaining tissue or fluid samples from the body.
In tissue biopsy, for example, a needle (or puncturing cannula) is inserted into the body and guided to the site of the tumor or other tissue mass to be evaluated. The physician guides the needle to the desired location in the body using an imaging system such as ultrasound, which permits the physician to monitor the insertion and advancement of the needle in the body. Ultrasound guidance systems are well known in the art, and work on the principle of reflecting sound waves off of the needle. The reflected wave is detected by a monitor located outside the body, and an image is generated, which reveals the location of the needle in the body. Two examples of ultrasonically guided puncturing cannula apparatuses are found in U.S. Pat. No. 3,556,079 and U.S. Pat. No. 4,029,084, the disclosures of which are incorporated herein by reference. Needle guidance with ultrasound imaging may be used to obtain tissue and fluid samples in a variety of procedures such as, for example, para and thoracocenteses, amniocentesis, abscess aspiration, cytologic and core histologic biopsy, and fetal blood sampling.
Accurate guidance of the needle in the body is not only critical to obtaining the proper tissue sample, but accurate guidance is also necessary to avoid unintentional puncturing or damage to body tissue. Unfortunately, needles conventionally used in biopsy procedures and the like that rely on ultrasonic imaging for guidance have relatively poor ultrasonic visibility. The needles conventionally used in such procedures have a generally tubular shape with a circular cross-section, and thus present a curved surface to the incident ultrasonic beam. When the incident beam strikes the curved surface of these conventionally shaped circular needles, only a small portion of the beam is reflected back to the monitoring device; a majority of the incident beam being scattered away from the monitoring device. Because only a small portion of the reflected incident beam is detected at the monitoring device, a relatively poor image of the needle is generated, which makes it difficult to ascertain the precise position of the needle in the body. In response to this problem, considerable effort has been expended to enhance the ultrasonic visibility of conventionally shaped circular needles.
For example, one prior approach to enhancing the ultrasonic visibility of the needle is roughening or scouring the outer surface of the needle itself or by roughening the surface of a solid stylet that is disposed axially within the lumen of the needle. One such example of this approach is found in U.S. Pat. No. 4,869,259, the disclosure of which is incorporated herein by reference. A portion of the exterior surface of the needle is uniformly and randomly particle-blasted with particulate materials such as sand, silicon carbide, or metal silicates. The resulting particulate band, which extends around the circumference of the needle, increases its ultrasonic visibility by causing diffraction of the reflected incident beam as the angle between the needle and the incident beam is deviated from 90 degrees.
Another example of an attempt to make a needle more ultrasonically visible is found in U.S. Pat. No. 4,401,124, the disclosure of which is incorporated herein by reference. This patent discloses a surgical instrument having diffraction grating disposed on the surface of the instrument. The grating has a specific distance between the depths of adjacent grooves, the distance being a function of various parameters including the wavelength of the incident beam and the angle between the incident beam and an axis along the surface of the instrument. It is disclosed that the diffraction grating increases the reflection coefficient of the surgical instrument, which increases its ultrasonic visibility.
Although these prior art approaches may improve the ultrasonic visibility of a needle, the process of roughening or scouring the needle adds additional steps to the manufacturing process, and increases manufacturing costs. Also, a scoured or roughened needle surface may complicate percutaneous insertion and subsequent passage of the needle through body tissue.
Another approach to increasing the ultrasonic visibility of a needle is disclosed in U.S. Pat. No. 5,048,530, the disclosure of which is incorporated herein by reference. That patent discloses a needle or other tubular cannula having one or more "sounding apertures" positioned along the needle to improve its ultrasonic visibility. The diameter of each sounding aperture is substantially equal to a predetermined wavelength of an incident ultrasonic beam. According to the disclosure of the patent, upon striking the sounding aperture, the incident beam is diffracted and the resulting echo diffuses isotopically therefrom, thereby improving the ultrasonic detectability of the needle. Again., as with other prior art approaches, the sounding aperture approach may make the needle more difficult to manufacture and increase manufacturing costs.
Another approach to improving the ultrasonic visibility of a needle is to place a transducer in the needle itself to radiate an ultrasonic beam back to a detector located outside the body. However, a shortcoming to this approach is that the needle must be equipped with expensive and complicated electronic circuitry, which increase the complexity of and the cost to manufacture the needle.
Clearly, there is a need for a medical instrument, and a needle in particular, with enhanced ultrasonic visibility, and which is inexpensive and simple to manufacture.